FIG. 1 renders detailed (magnified) views of aspects of a particular embodiment of a sample S that can be used in conjunction with the present invention. This particular type of sample S comprises what is often referred to as a “grid” or “Autogrid” G. It comprises a circular ring 21a of wire (e.g. comprising Cu or Ni, for instance), the diameter of the ring typically being of the order of about 3 mm and the diameter of the wire typically being of the order of about 20-100 μm. Attached within the ring 21a are straight wire portions 21b, which are (in this case) arranged to form an orthogonal grid pattern, thus defining a matrix-like array of (substantially square) apertures (openings/holes/windows) 23. The middle portion of FIG. 1 shows a transverse cross-sectional view of the upper portion of the Figure, taken along the diameter B-B′. It shows that the grid G has a substantially planar (plate-like) form, with opposed first (S1) and second (S2) “faces” substantially parallel to one another. As here depicted, a membrane 25 has been spanned upon the first face S1 (and, optionally, affixed to the wires 21b, e.g. using an adhesive or by molten bonding). This membrane 25 may, for example, comprise a carbonaceous material such as nylon or graphene, and will typically have a thickness (in the Y direction) ranging from about 0.3 nm to hundreds of nm. The membrane 25 contains a distribution of perforations 27, which are clearly visible in the detailed view at the bottom of the Figure. These perforations 27 typically have a diameter (parallel to the XZ plane) in a range of ca. 1.2-3.5 μm (e.g. ˜2 μm). In essence, the grid G acts as a scaffold for the membrane 25, and the membrane 25 in turn acts as a supporting structure for the perforations 27 (so that it is sometimes referred to as a “holey carbon support”). It is within the perforations 27 that the ultimate “specimen” is to be provided and supported—in the form of a thin film 29 of aqueous liquid (comprising one or more study specimens suspended therein) that is spanned across each given perforation 27, remaining in place (inter alia) by virtue of surface tension effects. It should be noted that structures as depicted in FIG. 1 (grid G+perforated membrane 25, 27) and as described above are commercially available, e.g. from firms such as Ted Pella, Inc., of Redding, Calif., USA. It is also possible to purchase (a variety of) pre-manufactured holey carbon films (corresponding to the perforated membrane 25, 27), e.g. from firms such as Quantifoil Micro Tools GmbH, Jena, Germany. Inter alia in the context of the present invention, the illustrated structure can be regarded as having a “backside” Sb and a “frontside” Sf.
A film 29 of aqueous liquid can be provided in the various perforations 27 of the membrane 25 using methods well described in technical literature and known to the skilled artisan. In one such known method, a sheet of blotting paper (not depicted) is pressed against the outer/lower surface of membrane 25, is then moistened with the aqueous liquid in question, and is subsequently removed (e.g. peeled off) of the membrane 25—causing (most of) the apertures 27 to be endowed with a (mini-)film 29 of the aqueous liquid, which is spanned within them by surface tension effects. A method of this type is described, for example, in the article Cryo-negative Staining by Marc Adrian et al. in Micron 29 (2-3), Elsevier Science Limited, 1998, pp. 145-160, and will not receive further attention here. Reference is also made to an alternative method that is set forth in U.S. Pat. No. 9,772,265 (with the same inventor/assignee as the present application, and incorporated herein by reference).
Turning now to FIG. 2, this shows a particular sample of a type such as that illustrated in FIG. 1, after vitrification using the method set forth in the aforementioned U.S. 2017/0169991 A1 (same flush applied to backside and frontside of sample). The dark/mottled squares/cells are undamaged or only somewhat damaged (successful vitrification procedure), whereas the white squares/cells correspond to locations where membrane breakage/de-lamination has occurred (to a greater or lesser extent). In the current situation, it is seen that of the order of ca. 50% of the squares/cells are sub-optimal. As set forth above, closer examination of the sample (not evident in the current Figure) reveals that the damaged squares/cells have been detached with a prevalent backside-to-frontside directionality.